Enhanced Continental Weathering as a Trigger for the End-Devonian Hangenberg Crisis

The Hangenberg Crisis coincided with a large decline of biodiversity and widespread anoxia in the end-Devonian ocean. Previous research attributed marine anoxia to the spread of deeply-rooted plants and/or increased volcanism on the continents, but crucial links have not been thoroughly explored. Herein, we propose enhanced weathering as a key trigger, as evidenced by a negative shift (similar to 8 parts per thousand) in lithium isotopes and a coupled response in carbon isotopes of marine carbonates in South China. Our findings imply that rapid weathering of crustal rocks increased nutrient delivery to the ocean, as indicated by an increase in the carbonate-associated phosphate levels, contributing to oceanic eutrophication. In the absence of massive volcanic emissions and intense orogeny, the cause of enhanced continental weathering was likely the expansion of the terrestrial rhizosphere, highlighting the potential for land plant evolution to initiate weathering changes of sufficient severity to trigger a major bio/environmental crisis in the Earth system.